1. Field of the Invention
The present invention relates to a resin-coated optical fiber, with glass optical fiber coated with UV-curing resin.
2. Description of the Related Art
As shown in FIG. 10A, conventionally known resin-coated optical fiber is a resin-coated optical fiber 200 with a two-layer resin structure in which an outer periphery of a glass optical fiber 201 composed of a core 211 and a clad 212, is sequentially coated with a primary layer 202 with low Young's modulus, and a secondary layer 203 with high Young's modulus, which are made of UV-curing resin (described as UV-resin hereafter) (for example, see patent document 1). The primary layer 202 in contact with the glass optical fiber 201 is a soft UV-resin layer with Young's modulus of about 0.1 MPa to 1.5 MPa, and the secondary layer 203 is a UV-resin layer with a hard shell structure with Young's modulus of about 600 MPa to 2000 MPa. With such a two-layer resin structure of the primary layer 202 and the secondary layer 203 with different Young's modulus, shock of an external stress such as a lateral pressure added to the glass optical fiber 201 is relaxed and absorbed when the resin-coated optical fiber 200 is bent, to thereby suppress an increase of a transmission loss such as a micro bending loss of the optical fiber.
Further, patent document 2 discloses a method of adding a silane coupling agent to the primary layer 202 in contact with the glass optical fiber 201 for suppressing a progress rate of glass corrosion caused by OH-group on the surface of the glass optical fiber 201. The silane coupling agent is brought into a dehydration condensation by metalloxane bond or silanol bond with the OH-group on the surface of the glass optical fiber 201, thereby suppressing the progress of the glass corrosion by reducing the OH-group.
[Patent Document 1]
    Japanese Patent Laid Open Publication No. 2001-83381[Patent Document 2]    Japanese Patent Laid Open Publication No. 2003-95706
However, in the resin coated optical fiber with the aforementioned two-layer resin structure, suppressing an increase of the transmission loss such as micro bending loss of the glass optical fiber by relaxing and absorbing the external stress, and realizing a long-term reliability by maintaining a fracture strength of the glass optical fiber for a long time, are difficult to be compatible with each other, even if Young's modulus of the UV-curing resin of the primary layer 202 and the secondary layer 203 is variously changed.